1. Field of the Invention
The present invention relates to a thin-film magnetic head (magnetoresistive head) for reading (and writing) information with high-density recording by utilizing the magnetoresistive effect, and a method of forming the thin-film magnetic head.
2. Description of the Related Art
A thin-film magnetic head for reproduction includes, in its basic structure, a multilayered film developing the magnetoresistive effect between an upper shielding layer and a lower shielding layer, which are formed above an AlTiC substrate. A thin-film magnetic head is also known which is constituted as a recording/reproducing head by forming, on the thin-film magnetic head for reproduction, a thin-film inductive head for recording (magnetoresistive recording head). Roughly speaking, the thin-film magnetic head for recording and reproduction is constructed by successively forming a lower shielding layer, a lower gap layer, a magnetoresistive sensor, an upper gap layer, an upper shielding layer, and a lower core layer (in the case of a piggyback type structure) (or, as an alternative, a merged type structure is obtained in which the upper shielding layer serves also as the lower core layer), and then by successively forming, on the lower core layer, a magnetic pole section and a coil layer both positioned to locate in an Air Bearing Surface (ABS), a gap layer, an upper core layer, and a barrier layer.
In the process of manufacturing such a thin-film magnetic head for reproduction and a thin-film magnetic head for recording and reproduction, a magnetic film serving as the lower shielding layer has been formed over an entire substrate surface in the past. However, it is a recent prevailing tendency to reduce an area in which the lower shielding layer is formed (i.e., to form a partial lower shielding layer) for the purpose of either reducing the probability of a short-circuit with a wiring pattern of a multilayered film or improving the reproduction performance.
Hitherto, such a partial lower shielding layer has been formed through the following steps. On an AlTiC substrate having a substrate protective layer made of alumina (Al2O3), a resist is formed by photolithography to define an area in which the lower shielding layer is to be formed. Then, a soft magnetic material constituting the lower shielding layer, such as Permalloy (NiFe), is plated (by frame plating) over the entire substrate surface under a magnetic field. After removing useless layers including the resist, an alumina film is formed over the entire substrate surface including the lower shielding layer. Then, the alumina is scrapped off by a Chemical Mechanical Polishing (CMP) step until the lower shielding layer is exposed.
The above-described conventional method of forming the partial lower shielding layer, however, essentially requires expensive equipment and an additional step for forming an alumina film. Also, a strong-acid slurry is usually employed in the polishing CMP step of scraping off the alumina film until the lower shielding layer is exposed. However, because polishing rates of alumina and a soft magnetic material, such as Permalloy, are substantially equal to each other, it is typically difficult to control the film thickness of the lower shielding layer (i.e., deciding when to end the CMP step). Further, the alumina surface is typically corroded and roughed with the use of a strong-acid slurry. In addition, in a photolithography step of forming a resist layer to define a track width of a magnetoresistive sensor, a film thickness distribution of the resist layer is not uniform and a variation may occur in the track width of the magnetoresistive sensor.